systemd/systemd: introduce systemd-tests subpackage

Then, we can run unit tests and integration tests on postmarketOS systems.

Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/8718>

extra-repos/systemd/systemd/APKBUILD

@@ -156,6 +156,7 @@ subpackages="
 	$pkgname-dbg
 	$pkgname-dev
 	$pkgname-doc
+	$pkgname-tests
 	$pkgname-x11
 
 	$pkgname-udevd
@@ -245,6 +246,7 @@ build() {
 		-Dpamlibdir=/usr/lib/security \
 		-Dpamconfdir=/usr/lib/pam.d \
 		-Dinstall-sysconfdir=false \
+		-Dinstall-tests=true \
 		\
 		-Dsysupdate=enabled \
 		-Dsysupdated=enabled \
@@ -497,6 +499,12 @@ journald_zcomp() {
 	_default_zshcomp _journalctl
 }
 
+tests() {
+	depends="$pkgname=$pkgver-r$pkgrel"
+
+	amove usr/lib/systemd/tests
+}
+
 x11() {
 	pkgdesc="systemd x11"
 	install_if="$pkgname=$pkgver-r$pkgrel xorg-server-common"